Figure 4.

(a) AFM images of curved structures with various interspacings of adjacent nanobumps from 300 to 900 nm. Images (b) and (c) are the TIRM images of the concave (left column) and convex (right column) curved structures with different interspacings at the focal planes of Au film and z = 3.62 μm. The SPP wave propagates along the +y direction. (d) Optical intensity profiles of focusing patterns measured from (c) along the cross section lines, which are depicted in upper-left insets. For the convex structure at z = 3.62 μm, there are five different curves corresponding to 300- to 900-nm interspacings of adjacent nanobumps, respectively. The upper-right inset shows the intensity of the central peak as a function of interspacings of nanobumps.